Electron transfer rate of redox ion controlled by electrostatic interaction with bilayer films assembled using thiolate-copper ion-carboxylate bridges

11-mercaptoundecanoic acid (MUA) monolayer and MUA-copper ion-MUA bilayer assembled using thiolate-coppcr ion-carboxylate bridges on MUA monolayer electrode were prepared, and tried to control electron transfer rate of redox ions. The soaking solution to assemble MUA on gold electrode changed from ethanolic MUA solution to 1-butanolic one, then the differential interfacial capacitance decreased from 2.5±0.1 μF cm⁻² to 1.6±0.2 μF cm⁻², and electron rate constant, k⁰ of [Co(phen)₃]³⁺ decreased from 20×10⁻⁶ cm s⁻¹ to 8.3×10⁻⁶ cm s⁻¹. These results show that highly ordered MUA monolayer can be obtained only changing soaking solvent to assemble MUA, Obtained highly ordered MUA monolayer electrode was block off completely redox anion by electrostatic repulsion and MUA film thickness. Moreover using MUA-copper ion-MUA bilayer electrode, k⁰ of [Co(phen)₃]³⁺ decreased under 1/400 against using MUA monolayer electrode, that value become to under 0.02×10⁻⁶ cm s⁻¹. This study shows that the combination of electrode surface charge and length of insulating spacers is able to control electron transfer rate of various electroactive ions.     

XPS and flow-cell EQCM study of albumin adsorption on passivated chromium surfaces: Influence of potential and pH

The adsorption of albumin (BSA: bovine serum albumin) on passivated chromium surfaces was studied in deaerated sulphate solutions as a function of potential (in the passive state) and pH (from 4 to 10). In situ switch-flow cell EQCM measurements were coupled to ex situ XPS analyses. EQCM results showed that (i) the initial adsorption rate is about 3.3 ng cm⁻² s⁻¹ which corresponds to 3 × 10¹⁰ molecules cm⁻² s⁻¹, irrespective of the passive potential and pH, and (ii) the passive potential as well as the pH have no influence on the amount of adsorbed BSA (Δm = 440 ± 70 ng cm⁻² on the adsorption plateau). From the XPS N 1s and C 1s signals, which provide a fingerprint for the protein, it can be concluded that BSA is adsorbed on the Cr surface and is chemically intact. The XPS results show that (i) when increasing the passive potential, the oxide layer thickness increases (mean value: d_ox = 2.2 ± 0.2 nm), and (ii) the passive film is not modified by the adsorption of protein. From combined EQCM and XPS data, a full coverage of the Cr surface by the adsorbed proteins (γ = 1) is demonstrated at pH 4 (whatever the passive potential). The thickness of the continuous BSA layer (h_BSA) is 3.3 ± 0.3 nm, which corresponds to one monolayer “side-on”, i.e. oriented parallel to the surface. At pH 5.5 and 10, the adsorbed proteins form islands. The surface coverage is much lower (γ ∼ 0.5), and the height of the protein islands is significantly higher (h_BSA ∼ 6.5 nm). The results suggest a strong interaction (partially covalent) between the protein and the passivated chromium surface.     

Rapid formation of high-quality self-assembled monolayers of dodecanethiol on polycrystalline gold under ultrasonic irradiation

Self-assembled monolayers of dodecanethiol (C₁₂SH-SAMs) on polycrystalline gold were prepared under ultrasonic irradiation at 100 W (the actual ultrasonic power intensity is about 0.1 W cm⁻² including the heat loss) for different time and investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). CV experiments show that the differential capacitance C_d values of the C₁₂SH-SAM prepared under ultrasonic irradiation at 100 W (0.1 W cm⁻²) for 15 min are independent of the scan rate, the thickness d value of this monolayer is 17.5 Å, the tilt angle φ value of the molecules in this monolayer from the gold surface normal was calculated to be 30° and the difference value of the current density at −0.2 and 0.5 V (Δi_p) is only 0.69 μA cm⁻². From the EIS experiments, we find that the phase angle value at 1 Hz Φ_1 Hz of the C₁₂SH-SAM prepared under ultrasonic irradiation at 100 W (0.1 W cm⁻²) for 15 min is 89°, the charge transfer resistance R_ct value of this monolayer is 1.40 × 10⁶ Ω cm² and the surface coverage θ value of this monolayer was calculated to be 99.997% from R_ct. These results indicate that the C₁₂SH-SAM of almost defect-free structure and very low ionic permeability can be formed under ultrasonic irradiation at 100 W (0.1 W cm⁻²) in a short time (15 min).     

Electrogravimetric investigation of formaldehyde oxidation at Pt electrodes in acidic media

The electrochemical and adsorptive behavior of formaldehyde at Pt electrodes in acidic media was investigated using cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (EQCM) techniques. All chemical and electrochemical steps related to formaldehyde oxidation (e.g. bulk adsorption and oxidation, CO (sub)monolayer adsorption and oxidation and electrons per Pt site) were analyzed. All the mass and charge density data in this paper are referred to the real surface area. The charge density associated with formaldehyde oxidation was close to 420 μC cm⁻², which is related to the oxidation of approximately one CO monolayer with two electrons transferred. For CO adsorption the experimental mass value was 50 ng cm⁻². In the region of CO oxidation the analysis of mass and charge variations indicates simultaneous CO oxidation, anion and water adsorption and CO readsorption. The mechanism was confirmed by CO and CO₂ flux calculations. From the analysis of the mass-charge ratio and species flux it was concluded that CO, an intermediate produced during formaldehyde oxidation, is adsorbed at the Pt surface and the main contribution to the mass increase during formaldehyde oxidation is CO readsorption, and water adsorption.     

A voltammetric and nanogravimetric study of Te underpotential deposition on Pt in perchloric acid medium

This work describes the study of Te underpotential deposition on Pt in acid media using cyclic voltammetry, rotating ring-disc electrode and electrochemical quartz crystal microbalance techniques. The voltammetric results indicate the presence of two dissolution peaks in the positive scan with a total charge density of 420 μC cm⁻². These phenomena are attributed to the deposition of one Te monolayer with the occupancy of two active Pt sites by each ad-atom. This is confirmed by rotating ring-disc electrode results. The electrochemical quartz crystal microbalance (EQCM) experiments yielded the small mass variation of −32 ng cm⁻² (while the theoretical one is −140.4 ng cm⁻² for a complete Te monolayer). This low value can be attributed to the simultaneous adsorption of water, perchlorate anions and the formation of platinum oxide.     

Investigation of a protective conducting silica film on n-silicon

This paper concerns an attempt to dope a protective SiO₂ layer on n-Si so that the latter could act as a stable photo-anode. A SiO₂ film was electrochemically grown over an n-Si surface on which a submonolayer amount of Pt had been deposited. Thereafter the electrode was subjected to a heat treatment. There resulted an electrode which was photoactive for more than 100 h.Pt is present in the film at 0.25 (at Si/SiO₂) to 0.03 (SiO₂/solution) atomic per cent. Its form is as Pt and PtO. The energy level of the Pt is close to the n-Si valence band edge.The photocurrent density passes through a maximum when the Pt present in the film corresponds formally to 0.25 monolayer. Higher activities probably cannot be obtained because Pt also diffuses into Si and causes recombination of hole-electron pairs. An indirect estimate of the film resistance shows a specific conductance of 10^?9 mho cm^?1. The corresponding mobility would be around 10^?7 cms^?1 (V cm^?1)^?1 and hence too small for a charge carrier in band conduction. It is suggested that electrons tunnel between Pt atoms. A 30% decrease of photocurrent in 100 h is probably due to residual film growth. The approach has advantages but requires the seeking of improved doping.     

Ferroelectric Photocurrent Effect in Polycrystalline Lead‐Free (K0.5Na0.5)(Mn0.005Nb0.995)O3 Thin Film

We deposited (K_0.5Na_0.5)(Mn_0.005Nb_0.995)O₃ (KNMN) thin films on Pt(111)/TiO₂/SiO₂/Si(100) substrates with a top electrode of indium tin oxide and investigated photocurrent properties in the wavelength range of 300?400 nm. Before the photocurrent measurement, the KNMN film was poled by applying a DC voltage. The photocurrents strongly depend on the wavelength of the incident photon energy. The photocurrents of the first measurement with poling in the up (?5 V) and down (+5 V) states were 21 and 3.2 nA/cm², respectively, at 344 nm. The difference in the photocurrents in both poling directions was explained by a space charge due to an asymmetric Schottky barrier height, which was caused by an internal electric field and polarization in the KNMN thin film.     

Chlorophyll assembled electrode for photovoltaic conversion device

Chlorophyll-a (Chl-a) assembled in hydrophobic domain by fatty acid with long alkyl hydrocarbon chain such as myristic acid (Myr), stearic acid (Ste) and cholic acid (Cho) modified onto nanocrystalline TiO₂ electrode is prepared and the photovoltaic properties of the nanocrystalline TiO₂ film by Chl-a are studied. Incident photon to current efficiency (IPCE) value at 660 nm in photocurrent action spectrum of Chl-a/Ste-TiO₂, Chl-a/Myr-TiO₂ and Chl-a/Cho-TiO₂ electrodes are 5.0%, 4.1% and 4.1%, respectively. Thus, the IPCE is maximum using Chl-a/Ste-TiO₂ electrode. From the results of photocurrent responses with light intensity of 100 mW cm⁻² irradiation or monochromatic light with 660 nm, generated photocurrent increases using Chl-a/Ste-TiO₂ electrode compared with the other Chl-a assembled TiO₂ electrodes. These results show that the hydrophobic domain formed by stearic acid with long alkyl hydrocarbon chain is suitable for fixation of Chl-a onto TiO₂ film electrodes and photovoltaic performance is improved using Chl-a onto Ste-TiO₂ film electrode.     

The potentiodyanmic formation and reduction of a silver sulfide monolayer on a silver electrode in aqueous sulfide solutions

A potentiodynamic study of silver electrodes in aqueous sulfide solutions, carried out to form phase silver sulfide films, revealed that a monolayer of silver sulfice forms as a distinct and separate stage of film growth at an underpotential of about 0.12 V. The monolayer peak (and its cathodic counterpart) was also characterized by a linear relationship between peak current density and potential sweep rate and a constant charge density of about 0.2 mC/cm². The potentiodynamic E/i curves for the silver sulfide monolayer were simulated by computer on the basis of a mechanism of the initial adsorption of HS^? on the silver surface in a fast equilibrium step followed by a rate determining electron transfer step to form AgHS as a surface intermediate. The AgHS species then rapidly diffuses on the surface and joins a growing two-dimensional silver sulfide monolayer nucleus. Under the experimental conditons studied here, the formation and reduction of the silver sulfide monolayer was found to be of intermediate kinetic reversibility.     

Organic dyes incorporating the cyclopentadithiophene moiety for efficient dye-sensitized solar cells

Three triarylamine organic dyes (XS28-30) containing a cyclopentadithiophene unit as the conjugated bridge have been designed and synthesized for a potential application in dye-sensitized solar cells (DSSCs). Their absorption spectra, electrochemical and photovoltaic properties have been investigated. The incorporation of ethyl-substituted cyclopentadithiophene is highly beneficial to light-harvesting and preventing close π-π aggregation, thus favorably generating high efficiency. For a typical device, a solar energy conversion efficiency (η) of 5.8% based on XS29 was achieved under simulated AM 1.5 solar irradiation (100 mW cm⁻²) with a short-circuit photocurrent density (J_SC) of 14.4 mA cm⁻², an open-circuit voltage (V_OC) of 601 mV, and a fill factor (ff) of 0.68. These results suggest that the functionalized cyclopentadithiophene unit is a promising candidate for DSSCs.     

In situ quaterizable oligo-organophosphazene electrolyte with modified nanocomposite SiO2 for all-solid-state dye-sensitized solar cell

Two latent chemical cross-linked precursors: (1) oligo-organophosphazene with propionitrile and iodo-(ethylene oxide-co-propylene oxide) and (2) oligo-organosiloxane grafting oligo-ethylene oxide and propylene oxide dimethylamine are synthesized to form all-solid-state polymer electrolyte for dye-sensitized solar cells employing in situ quaterization reaction. This novel electrolyte shows about 6.79 × 10⁻⁷ cm² s⁻¹ of the apparent diffusion coefficient of triiodide. The disintegrating temperature of 181 °C demonstrates good thermal stability of the solid-state electrolyte. Proper amount of 7 nm SiO₂ modified with 3-triethoxysilylpropyl oligo(oxyethylene-co-oxypropylene) monomethyl urethane is added to the electrolyte and the photocurrent conversion efficiency reaches 2.66% compared with that of 1.81% with no additive.     

Adsorption of bromo-phenol blue from an aqueous solution onto thermally modified granular charcoal

The adsorption phenomenon of bromo-phenol blue onto pristine and thermally evacuated granular charcoal (GC) was studied via a batch technique at 25 °C. The effect of evacuation temperature on the GC surface and pore structure (e.g. pore volume and diameter) was studied by Fourier transform infrared spectroscopy (FT-IR), point of zero charge (PZC), proximate analysis, Brunauer, Emmett and Teller (BET) method and field emission scanning electron microscopy (FE-SEM). The FT-IR spectra of the samples after evacuation showed considerable decrease in the acidic functional groups. PZC showed that the surface of the evacuated charcoal became basic as the evacuation temperature was increased from 300 to 800 °C. Volatile matter decreased while ash and fixed carbon contents increased during evacuation, which led to an increase in the micro-pore volume from 0.25 to 0.42 cm³ g⁻¹, meso-pore volume from 0.04 to 0.13 cm³ g⁻¹, pore diameter from 5.01 to 6.21 nm, and specific surface from 150.32 to 254.70 m² g⁻¹. Adsorption of the bromo-phenol blue onto charcoal, increased as the evacuation temperature was increased from 300 to 800 °C. The interaction of bromo-phenol blue with charcoal was proposed to have occurred via hydrogen bonding. The adsorption data fitted well with the Langmuir equation, which indicated that the monolayer adsorption has occurred at specific sites within the adsorbent.     

Effect of particle size and surface area on the adsorption of albumin-bonded bilirubin on activated carbon

The adsorption behavior of albumin-bonded bilirubin on different micrometer-sized granular activated carbons (GACs) with different BET surface areas of 913, 1173 and 1413 m² g⁻¹ and different pore size distributions in the micropore and mesopore range has been investigated in order to study the behavior of bilirubin from batch experiments. The extent of adsorption was measured from the residual concentrations of bilirubin in the solution after different adsorption times using visible absorption spectroscopy. It has been demonstrated that the adsorption rate of bilirubin increases with decreasing particle size and with increasing mesopore volume which was obtained from benzene isotherms. A diffusion coefficient of about D = 0.60 × 10⁻¹⁰ cm² s⁻¹ for bilirubin adsorption on activated carbon particles with a benzene mesopore volume of 0.18 cm³ g⁻¹ in the pore range of 2.35-44.0 nm was calculated from the Fick’s law of diffusion by using an intraparticle mass transfer model of sorptive uptake from a stirred solution of limited volume in spherical particles.     

Electrochemically multi-anodized TiO2 nanotube arrays for enhancing hydrogen generation by photoelectrocatalytic water splitting

An enhanced hydrogen production by photoelectrocatalytic water splitting was obtained using extremely highly ordered nanotubular TiO₂ arrays in this work. Highly ordered TiO₂ nanotube arrays with a regular top porous morphology were grown by a facile and green three-step electrochemical anodization. The well ordered hexagonal concaves were uniformly distributed on titanium substrate by the first anodization, served as a template for further growth of TiO₂ nanotubes. As a result, the TiO₂ nanotube arrays constructed through the third anodization showed appreciably more regular architecture than that of the sample by conventional single anodization under the same conditions. The enhanced photoelectrochemical activity was demonstrated through the hydrogen generation by photoelectrocatalytic water splitting, with an exact H₂ evolution rate up to 420 μmol h⁻¹ cm⁻² (10 mL h⁻¹ cm⁻²) in 2 M Na₂CO₃ + 0.5 M ethylene glycol. The photocurrent density of the third-step anodic TiO₂ nanotubes is about 24 mA cm⁻² in 0.5 M KOH, which is 2.2 times higher than that of the normal TiO₂ nanotubes (∼11 mA cm⁻²) by a single electrochemical anodization.     

Electrocatalytic oxidation of deoxyguanosine on a glassy carbon electrode modified with a ruthenium oxide hexacyanoferrate film

The electrocatalytic oxidation of deoxyguanosine on a ruthenium hexacyanoferrate (RuOHCF) glassy carbon (GC) modified electrode was investigated in acid medium by using rotating disc electrode (RDE) voltammetry. Chronoamperometric experiments allowed information on the charge transport rate through the RuOHCF film and at a very short time window a diffusion-like behavior was observed with a D_ct value of 2.7 × 10⁻¹¹ cm² s⁻¹ for a film with Γ = 4.47 × 10⁻⁹ mol cm⁻². The influence of systematic variation of rotation rate, film thickness and the electrode potential indicates that the rate of cross-chemical reaction between Ru(IV) centers immobilized into the film and deoxyguanosine controls the overall electrodic process and the value of the rate constant was found to be 3.2 × 10⁶ mol⁻¹ L¹ s⁻¹. The relatively high rate constant of the cross-reaction, the facile penetration of the substrate through the film and the fast transport of electrons suggest that the electrocatalytic process occurs throughout the film layer.     

On the determination of kinetic characteristics of lithium intercalation into carbon

The diffusional processes proceeding in the intercalation electrode on applying a potential step are theoretically treated. The theory of chronovoltammetry is shown to require the necessary account of the contribution of the surface solid-state film to the overall diffusion resistance of the electrode. For the case of small deviations from equilibrium, analytical solutions of the diffusion problem have been obtained. Ignoring the retarding contribution of the surface film is shown to bring about an error into the diffusion coefficient of lithium in its alloys and intercalates. The theory has been experimentally verified with Li_xC₆ electrodes of various compositions made of pyrocarbon films on a nickel backing as examples. The diffusion coefficients are 10⁻¹¹-10⁻⁹ cm² s⁻¹, depending on composition.     

Tris (2,2′-bipyridil) copper (II) chloride complex: a biomimetic tyrosinase catalyst in the amperometric sensor construction

The use of tris (2,2′-bipyridil) copper (II) chloride complex, [Cu(bipy)₃]Cl₂·6H₂O, as a biomimetic catalyst, is reported in the construction of an amperometric sensor for dopamine. The sensor was prepared modifying a glassy carbon electrode with a Nafion® membrane doped with the complex. The optimized conditions for the sensor response were obtained in 0.25 mol dm⁻³ Pipes buffer (pH 7.0) containing 150 μmol dm⁻³ H₂O₂, with an applied potential of −50 mV versus saturated calomel electrode (SCE). In these conditions, a linear response range between 9 and 230 μmol dm⁻³, with a sensitivity of 1.43±0.01 nA dm³ μmol⁻¹ cm⁻² and a detection limit of 4.8 μmol dm⁻³ were observed for dopamine. The response time for this sensor was about 1 s, presenting the same response for at least 150 successive measurements, with a good repeatability (4.8%) expressed as relative standard deviation for n=13. After its construction, this sensor can be used after 180 days without loss of sensitivity, kept at room temperature. The difference of the sensor response between four preparations was 4.2%. A detailed investigation about the sensor response for other eighteen phenolic compounds and five interfering species was performed. The sensor was applied for dopamine determination in pharmaceutical preparation with success.     

Micromolar determination of sulfur oxoanions and sulfide at a renewable sol-gel carbon ceramic electrode modified with nickel powder

The sol-gel technique was used to fabricate nickel powder carbon composite electrode (CCE). The nickel powder successfully used to deposit NiO_x thin film on conductive carbon ceramic electrode for large surface area catalytic application. Repetitive cycling in potential range −0.2 to 1.0 V was used to form of a thin nickel oxide film on the surface carbon composite electrode. The thin film exhibits an excellent electro-catalytic activity for oxidation of SO₃²⁻, S₂O₄²⁻, S₂O₃²⁻, S₄O₆²⁻ and S²⁻ in alkaline pH range 10-14. Optimum pH values for detection of all sulfur derivatives is 13 and catalytic rate constants are in range 2.4 × 10³-8.9 × 10³ M⁻¹ s⁻¹. The hydrodynamic amperometry at rotating modified CCE at constant potential versus reference electrode was used for detection of sulfur derivatives. Under optimized conditions the calibration plots are linear in the concentration range 10 μM-15 mM and detection limit 1.2-34 μM and 0.53-7.58 nA/μM (sensitivity) for electrode surface area 0.0314 cm². The nickel powder doped modified carbon ceramic electrode shows good reproducibility, a short response time (2.0 s), remarkable long term stability, less expense, simplicity of preparation, good chemical and mechanical stability, and especially good surface renewability by simple mechanical polishing and repetitive potential cycling. This sensor can be used into the design of a simple and cheap chromatographic amperometry detector for analysis of sulfur derivatives.     

In situ FTIR spectroscopic studies of (bi)sulfate adsorption on electrodes of Pt nanoparticles supported on different substrates

Nanostructured Pt electrodes were prepared by electrodeposition of Pt nanoparticles on different substrates (GC, Pt and Au) under cyclic voltammetric conditions and with various number (n) of potential cycling, and were denoted as nm-Pt/S(n) (S = GC, Pt and Au). Adsorption of (bi)sulfate on the nm-Pt/S(n) was studied by in situ FTIR reflection spectroscopy. It has been revealed that the nanostructured Pt electrodes exhibit anomalous IR properties for (bi)sulfate adsorption regardless of the different reflectivity of substrate, i.e. the IR absorption of (bi)sulfate species adsorbed on all the nm-Pt/S(n) electrodes is significantly enhanced and the IR band direction is completely inverted in comparison with the same species adsorbed on a bulk Pt electrode. The two IR bands around 1200 and 1110 cm⁻¹ attributed to adsorbed (bi)sulfate species are shifted linearly with increasing electrode potential, yielding Stark tuning rates () of 152.1 and 21.1 cm⁻¹ V⁻¹ on nm-Pt/GC(20), respectively. Along with increasing n, the Stark tuning rate of the IR band around 1200 cm⁻¹ decreases quickly and declined to 7.6 cm⁻¹ V⁻¹ on nm-Pt/GC(80), while the Stark tuning rate of the IR band near 1100 cm⁻¹ is fluctuated between 23.0 and 16.2 cm⁻¹ V⁻¹. It has determined that the enhancement of IR absorption of (bi)sulfate adsorbed on nanostructured Pt electrode is varied with substrate material and n, and a maximal 16-fold enhancement of the IR band near 1200 cm⁻¹ has been measured on the nm-Pt/GC(30) electrode. The in situ FTIR studies illustrated that the adsorption of (bi)sulfate occurs mainly in the double layer potential region, and reaches a maximum around 0.80 V. The results demonstrated also that the competitive adsorption of CO and oxygen species can inhibit completely (bi)sulfate adsorption, which has evidenced a weak interaction of (bi)sulfate with nm-Pt/S(n) electrode surface.     

Electrocatalytic oxidation of ascorbic acid by [Fe(CN)6] redox couple electrostatically trapped in cationic N,N-dimethylaniline polymer film electropolymerized on diamond electrode

Multinegatively charged metal complex, hexacyanoferrate ([Fe(CN)₆]⁴⁻), was electrostatically trapped in the cationic polymer film of N,N-dimethylaniline (PDMA) which was electrochemically deposited on the boron-doped diamond (BDD) electrode by controlled-potential electro-oxidation of the monomer. This ferrocyanide-trapped PDMA film was used to catalyze the oxidation of ascorbic acid (AA). Increase in the oxidation current response with a negative shift of the anodic peak potential was observed at the cationic PDMA film-coated BDD (PDMA|BDD) electrode, compared with that at the bare BDD electrode. A more drastic enhancement in the oxidation peak current as well as more negative shift of oxidation potential was found at the ferrocyanide-trapped PDMA film-coated BDD ([Fe(CN)₆]^3−/4−|PDMA|BDD) electrode. This [Fe(CN)₆]^3−/4−|PDMA|BDD electrode can be used as an amperometric sensor of AA. Ferrocyanide, electrostatically trapped in the polymer film shows more electrocatalytic activity than that coordinatively attached to the polymer film or dissolved in the solution phase. The electrocatalytic current depends on the surface coverage of ferricyanide, Γ_Fe, within the polymer film. Diffusion coefficient (D) of AA in the solution was estimated by rotating disk electrode voltammetry: D = (5.8 ± 0.3) × 10⁻⁶ cm² s⁻¹. The second-order rate constant for the catalytic oxidation of AA by ferricyanide was also estimated to be 9.0 × 10⁴ M⁻¹ s⁻¹. In the hydrodynamic amperometry using the [Fe(CN)₆]^3−/4−|PDMA|BDD electrode, a successive addition of 1 μM AA caused the successive increase in current response with equal amplitude and the sensitivity was calculated as 0.233 μA cm⁻² μM⁻¹.